IgM antibodies to oxidized phosphatidylserine as protection markers in cardiovascular disease among 60-year olds

Abstract

Objective: Phosphatidylserine is exposed on apoptotic cells and is prone to oxidation (OxPS). Here we analyze the association of IgM antibodies against OxPS (anti-OxPS) with the risk of cardiovascular disease (CVD).

Methods: Among sixty-year olds from Stockholm County in Sweden, previously screened for cardiovascular risk factors (2039 men, 2193 women), there were 210 incident CVD-cases identified during a 5-year follow-up. Using a nested case-control design, 622 age- and sex-matched controls were selected. Odds ratios (OR) with 95% intervals (CI) were calculated by conditional logistic regression. IgM anti-OxPS was measured by ELISA. Phagocytosis of apoptotic Jurkat-cells by macrophages was studied by flow cytometry.

Results: Anti-OxPS levels were lower among cases (median (interquartile range): 80.7 (60.9-101.0 vs. 84.6 (65.8-109.6); p = 0.047); among men (76.6 (55.8-99.2) vs. 82.0 (63.1-105.1); p = 0.022) and among women 89.6 (72.3-110.1) vs. 89.8 (69.9-114.4); p = 0.79). After adjustment for smoking, BMI, diabetes mellitus type II, hypercholesterolaemia and hypertension, and dividing into quartiles, using the highest quartile (quartile 4) as reference, quartile 3 was associated with a OR of 1.74 (CI 1.08-2.81). Quartiles 2 and 1 had similar associations, the later reaching statistical significance. Among men associations were stronger whereas no significant associations were observed in women. The OR of MI/angina comparing quartile 3 with quartile 4 was 2.31 (CI 1.30-4.11). The OR for quartile 2 and 1, respectively, were similar as for quartile 3. Total IgM increased uptake of apoptotic cells, which was reversed if incubated with OxPS.

Conclusions: IgM anti-OxPS is a novel potential protection marker for CVD, in particular in men. Increased phagocytosis of dying/dead cells could be one potential underlying mechanism.

Fig 1

a. Distribution of IgM anti-OxPS among cases and controls. 0 = controls who did not develop CVD during the follow up time, 1 = controls who did develop CVD. Cases hade significantly lower levels than controls (p = 0.047). Differences were more pronounced when highest quartile was compared with the other quartiles. b. Distribution of IgM anti-OxPS among women, cases and controls. 0 = controls who did not develop CVD during the follow up time, 1 = controls who did develop CVD. Cases hade significantly lower levels than controls (p = 0.047). Differences were more pronounced when highest quartile was compared with the other quartiles. c. Distribution of IgM anti-OxPS among men, cases and controls. 0 = controls who did not develop CVD during the follow up time, 1 = controls who did develop CVD. Cases hade significantly lower levels than controls (p = 0.047). Differences were more pronounced when highest quartile was compared with the other quartiles.

Fig 2. Effect on macrophage-mediated uptake of apoptotic cells.

Apoptotic jurkat cells were co-cultured with macrophages 5:1 with or without IgM, IgM which was either preincubated for 90 minutes or simultaneously added in the cell culture system as indicated. Phagocytosis assay was analyzed by flow cytometry. Phagocytosis of apoptotic cells was increased by total IgM but decreased by oxPS. Preincubation or simultaneous incubation of IgM with OxPS added to the cell culture systems further decreased the uptake of apoptotic cells. SFM = serum free medium; J = Jurkat-cells; M = Macrophages; OxPS = oxidized phosphatidylserine